HandBrake is an open-source, GPL-licensed, multiplatform, multithreaded DVD to MPEG-4 converter, available for MacOS X, Linux and Windows.

Supported sources:

Any DVD-like source: VIDEO_TS folder, DVD image or real DVD (encrypted or unencrypted, but protection methods other than CSS are not supported and must be handled externally with third-party software), and some .VOB and .TS files